Electric-furnace construction



W'. E. F. BRADLEY.

' ELECTRIC FURNACE CONSTRUCTION.

APPLICAHON FILED JULY 22,1918. RENEWED JAN. 25. I922.

1 55143 6. I Patented Aug. 29, 1922.

Flux

Gas 9 0 us Pr vducbs m fw 361 mto'awuaf UNITED STATES PATENT OFFICE.

WALTER E. F. BRADLEY, OF NYACK, NEW YORK.

ELECTRIC-FURNACE CQNSTRUCTIOH.

' Specification of Letters I'atent.

Patented Aug. 29, 1922.

Original application filed July 17, 1918, Serial No. 245,868. Divided and this application-filed July 22, 1918, Serial 110. 248,123. Renewed January 25, 1922. Serial 110. 531,822.

In the said prior application I have described a method andapparatus for-reducing iron'ore, including in the term ores, all materials containmg iron chemically united with oxygen, such as 'for example, hematite or other concentrates and the like.

The process described involves the use of an electric furnace for supplying heat to the material under treatment, while at the same time passing through the material ahydrocarbon gas, such as for example natural gas or methane. r

The invention contemplated by the present application resides in the mechanism or apparatus b which a reducing gas is introduced into t e material to be reduced and by which this material is supplied with the necessary heat.

As already explained in my said prior application, the introduction of a reducing gas into a molten mass of material requires for commercial considerations 3, tuyere of particular material, and the requirements are not satisfied by use of metal or ordinary re- 7 factory materials. It is also'necessary for ent invention will be more clearly understood from the description of a specific embodiment of the invention in an ore reduction "system;

The" accompanying drawing shows in purely diagrammatic form an ore reduction system in which an electric furnace constructed and operated in accordance with the invention is employed.

"In said drawing, 1 indicates an electric arc furnace, 2 the feed conduit normally connected with and leading thereto, 3 a rotary drum furnace discharging into said feed conduit 2, 4 the feed conduit for introducin to furnace 3 the ground flux and ore from oppers 5 and 6, while 7 may. representthe stack by which gaseous products of the system are finally discharged. Hoppers 5 and 6 are assumed to be properly supplied with finely divided flux and ore which pass therefrom into the supply conduit 4 from which they are introduced into the rotar drum furnace 3. In passing through .stage covers the mouth of tuyere 9, so that the gas passes upwardly through it. At the high temperature maintained by the electric arc between electrodes 10 and 11, the charge is ina state of fusion. I

The temperature at which-the hydrocarbon gas is here exposed, effects dissociation of the gas in the presence of the iron oxide, the chemical action involving the reduction of iron oxides by carbon and leaving the gas in the form of a mixture containing carbon monoxide and h drogen, as will be more fully explained hereinafter. The mixture containing the carbon monoxide and hydro gen is discharged through the mouth of the electric furnace into the feed conduit 2, and thence it passes into the rotary drum furnace 3 where the oreand flux are being mixed. These ases leaving the electric furnace 1 at a big temperature, and still possessin reducing properties, preheat the ore and ux which is being mixed within. the

rotary drum furnace 3, and effect apartial preliminary reduction of the iron oxide contained therein. Assuming, for example, the treatment of magnetite, the chemical action taking place within the preheating furnace 3 may be represented by the equation The remaining gas containing carbon monoxide, carbon dioxide, water vapor and free hydrogen, passes out through stack 7 and may be used as fuel to supply heat for any purpose.

Referring again to the final reduction which occurs inthe electric furnace 1, the chemical action may be represented as follows:

A flux which I have found satisfactory for the operations herein described, is one containing, or made up of sodium carbonnate or sodium chloride. The electric furnace is preferably of the basic lined type having for example, a lining of pure magnesia or magnesite brick. 0 protect this lining from attack by the flux or slag, it is desirable to maintain a basic condition in the slag. The sodium carbonate or chloride answers this purpose alone or it may be supplemented by additional basic material which need not have such low melting point,

such as lime, magnesia, or the like. The amount and composition of the flux depend on the amount of SiO,, A1 0,, and other impurities in the ore.

As already stated, the successful use of hydrocarbon gas as'a reducing agent, requires a particular construction and manipulation of the electric furnace, unimportant detail of which resides in the provision of a suitable form of tuyere through which the gas is introduced into the molten charge. I have found metal to be entirely unsuitable as a material for the construction of the tuyere, because of its high heat conductivity and relatively low fusion point. When artificially cooled, it tends to become stopped up. At the temperatures employed, it is chemically acted upon by the carbon or reducing agent. Tuyeres of refractory materials such as magnesia, silica and the like are chemically active, and furthermore are useless because they rapidly wear away or become stopped up. I find, however, that tuyeres. composed of carbon answer the requirements. They have comparatively low heat conductivity, withstand the high tem perature to which they are subjected, and are protected from chemical action with the charge by the atmosphere of reducing gas which is passing through them.

When the reductionis complete, it is necessary to stop the flow of gas through the charge, since to continue the supply of gas would alter the resulting composition f the steel or iron, and would not permit of separating the slag and :eel, due to the agitation. It is impossible to turn off the gas supplied to the tuyere while it is below the level of the liquid charge without causing the tuyere to stop up, therefore it is essential that the furnace be of the tilting type, so thatthe tuyere may be removed from below the level of the bath. The gas may then be turned oif completely or rtly as desired. The furnace is pneferab y arranged to have its intake or mouth suitably connected with the feed conduit 2 when the furnace is moved into receiving position, but permitting disconnection to be made for tilting the furnace and pouring off the slag and metal.

In the s stem shown, the supply of mixed ore and ux to the electric furnace takes place continuously over a considerable period of time during which the reduction is continuously roceeding. Thus the mixture is treated as ast as introduced and the entering fresh material is continuously delivered! u n the surface of the molten mass, where it is most directly exposed to the heat of the arc and thus most effectively acted upon. The introduction of heat from the electrodes above into the charge beneath is in this wa much more advantageously accomplishe than where the entire charge is introduced into the furnace before the heating stage begins. When the operations are proceeding properly and uniformly throughout the several parts of the system, the temperature within the electric furnace remains constant. As the various parts of the system are dependent upon each other with respect to chemical, thermal, and mechanical conditions uniformity of operation can be obtained by proper adjustment of the gas supply, the rate of feed, and the supply of electric power with respect to each other.

Having deoxidized the ore and obtained the metal in substantially pure form, the slag containing the impurities is poured off, after which the necessary additions are introduced to make the quality of steel desired and the heat continued long enough to obtain the necessary commingling of the ingredients into a uniform homogeneous state.

arbon, manganese, nickel and any other ingredients required to make steel of a specified analysis can be added as alloys or compounds. Carbon can also be added by passing an additional quantity of hydroca: bon gas through the steel after the removal of the slag.

By this process, it is possible to produce a very high grade of pure iron or steel of practically any analysis desired- I claim:

1. Reduction apparatus comprising in combination an electric furnace having suit said tuye're.

3. Reduction apparatus comprising in combination an electric furnace of the tilting type, provided with suitable electrodes and, having an outlet for pouring, and a carbon tuyere independent of said electrodes and disposed in position to be covered by the molten charge in the reducing position of the furnace and removed therefrom in the pouring position, and means for supplying a reducing gas to said tuyere. i

4.' An ore reduction apparatus comprising in combination an electric furnace of the tilting type provided with. suitable electrodes and having an inlet through which the charge is received and an outlet through which the slag and reduced charge may be poured, a rotary drum furnace having suitable communication with the electric fur nace inlet for delivering materials into the furnace and receiving gaseous products therefrom, a carbon tuyere independent of said electrodes and disposed in position to be covered by a molten charge in the electric furnace in the receiving and reducing position, and to be removed therefrom in the pouring position, and means for supplying a reducing gas to said tuyere.

WALTER E. F. BRADLEY. 

